1. Field of the Invention
The present invention relates to a method for making a non-oriented magnetic steel sheet having uniform magnetic characteristics and sheet shape in the coil product.
2. Description of the Related Art
Non-oriented magnetic steel sheets have been used in motors, dynamo-electric generators, and cores of transformers. Low core loss and high magnetic flux density are important magnetic properties required of non-oriented magnetic steel sheets, as these properties enhance the energy characteristics of the above-described devices.
A demand for less irregularity in motor characteristics has coincided with the recent development of motors which are highly controllable through integrated circuits. Thus, non-oriented magnetic steel sheets which possess uniform magnetic characteristics and sheet shape, especially sheet thickness in the coil product of a non-oriented magnetic steel sheet, are in great demand as motor core materials.
As a prior art method of producing uniform sheet thickness in the coil product, Japanese Patent Publication No. 57-60408 discloses a method which involves maintaining the finishing temperature of the hot rolling process within the .alpha.-phase temperature range. Furthermore, Japanese Patent Laid-Open No. 5-140649 discloses a steel containing extremely low quantities of N and S as a method of producing uniform sheet thickness in the coil product. However, these prior art techniques cannot produce the uniformity presently demanded, thus there remains a great need for marked improvement.